Fewer Wires, Lighter Cars

IEEE 802.3 Ethernet standard will reduce the weight of wires used in vehicles

By KATHY PRETZ12 April 2013

Photo: Molex

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Over the last 40 years, the hardware and associated software in cars have become quite sophisticated. The 1970s ushered in cruise control, check engine control, and electronic fuel injection. In the ’80s came antilock braking, climate control, and the heating and cooling of seats. Active cruise control, CD changers, dynamic stability control, navigation systems, and roll-stabilization systems were introduced in the ’90s. And the past decade has seen the addition of blind-spot warning systems, Bluetooth integration, Internet access, rearview cameras, and traffic-sign recognition.

Each feature calls for its own length of copper cabling to connect to one or more microcontroller units (MCUs), which sit at the heart of each electronic system. About 50 MCUs are found in mid-priced cars, almost 140 in high-end models. This cabling—and the harnesses involved—makes up the third heaviest and costliest component in a car, right behind the chassis and engine.

That’s why representatives from several car companies have joined the new IEEE P802.3bp Reduced Twisted Pair Gigabit Ethernet PHY (physical layer) Task Force. They are working toward a standard that defines an Ethernet physical layer and the performance characteristics of the data wiring. The plan is to use fewer than three twisted pairs of copper wires and the data rate of 1 gigabit per second. Reducing the number of wire pairs would make for many fewer wires and, hence, lighter and more fuel-efficient vehicles. And along with this will come simpler harnesses and the likelihood of lower costs.

The Ethernet PHY could form the backbone for all of an automobile’s data services, for everything from Bluetooth and driver assistance to vehicle-control systems such as those used in brakes, suspension, and transmission. This backbone will link many parts of the car, allowing data from one part to be reused elsewhere in the car.

“The automakers want to have a gigabit Ethernet with as few wires as possible,” says IEEE Member Steve Carlson, who chairs the study group. “They are completely rethinking how they do electronics and are moving to a network backbone just like the real world uses.

“The car companies looked at the most successful wired communications standards in the world and decided to use Ethernet, which has been deployed in billions of places around the world,” Carlson continues. “For automakers, that decision is really amazing: They decided to standardize on something they didn’t develop themselves.”

Networks are already used to some extent in today’s cars. They were developed by the car companies, and some are proprietary. These include the Controller Area Network, which has been around since 1981. It’s the dominant control bus in all vehicles, but it operates at a low speed: only 1 to 1000 kilobits per second. And FlexRay, which a handful of car manufacturers have used since 2005, operates at 10 megabits per second. Compared with gigabit Ethernet, it’s a “slow walk,” notes Carlson.

Some manufacturers have used the Media Oriented Systems Transport, known as MOST, since 2001. It’s a bus for streaming infotainment content and control data. Then there’s low-voltage differential signaling for point-to-point high-speed links (1 to 4 Gb/s) such as for cameras and displays, which has been in use since 2002. Typically, however, one manufacturer’s signaling system is incompatible with another’s.

Some car companies have been using Ethernet since 2008, but because of stringent limits on radio frequency interference, it is used only for diagnostics and firmware upgrades during vehicle servicing. And its 100-Mb/s speeds will not meet future bandwidth needs, according to Carlson.

“This is probably the first collaboration between the car industry and an IEEE standards group,” he says. “It’s a fascinating and challenging project, perhaps because we will have to fill in a lot of blanks.”

NEATER CABLING
The dozens of wiring harnesses in today’s vehicles are built one at a time on the assembly line. The workers snake the wires through cable pass-throughs located throughout the car—in the frame, in the door panels, under the carpeting, behind the dashboard, behind the taillights and inside the rear bumper, in the trunk, and elsewhere—and wrap them with protective material so they’re not damaged as the car moves along the line. This manual approach is tedious and time-consuming; it’s no surprise that labor accounts for half the cost of the harness. And with more features being added each new model year, the harnesses are getting bigger and heavier. The average is now about 100 kilograms.*

“The car manufacturers will be able to add more features without making the wiring harness any bigger or heavier,” Carlson says. “Rather, the harness will be slimmed down; instead of a dozen wires going off in every direction, signals will be carried on the network backbone.”

The earliest model year to see the IEEE 802.3 transceivers is 2019 because the carmakers work six years out, according to Carlson.

Cars aren’t the only mode of transportation that could benefit from these transceivers, he says. Freight, passenger, and bullet trains are heavily controlled by computers and electronics. And no industry has worse weight concerns than the airlines, which will also want to make use of fewer wires, he points out.

“This project is disruptive,” Carlson notes. “It could add huge new markets for Ethernet networking technologies, which will be good for silicon vendors and cable vendors as well.”